Single-Factor Authentication is a method of user authentication that requires the use of one authentication factor, the possession of something, in order to gain access to an account or service. The most common example of this is a password. The user must have possession of a password in order to gain access to the account or service.
The most common form of single-factor authentication is using one password, although some systems may allow you to use two passwords (a login and a password reset). A single-factor authentication system can also be used with other types of factors, such as biometrics (fingerprints), but by itself it provides little or no additional security over having one password alone.
Types of Single-Factor Authentication
There are two types of single-factor authentication:
Static: Static single-factor authentication (SSA) uses just one factor for every login attempt. For example, if you used only one password for all your accounts, this would be static SSA. This type is vulnerable to brute force attacks where an attacker tries every possible combination until they get it right.
Dynamic: Dynamic single-factor authentication (DSFA) uses different factors depending on the context in which they're used. For example, using a fingerprint scanner.